The present invention relates to magnetic tape cassettes. More particularly, the invention relates to the structure of a magnetic tape cassette in the hollow interior of which a magnetic tape is laid over a pair of tape winding cores and is guided to run in a predetermined direction to perform a recording or playback operation.
In the case where tape winding cores (hereinafter referred to as "hubs") with flanges are employed in a conventional magnetic cassette, the flanges of the hubs must have a certain thickness in view of manufacturing requirements, storage and mechanical strength. Accordingly, the hub is overall considerably thick and large in size. Thus, the use of flanged hubs is a significant obstruction against the further miniaturization of magnetic tape cassettes.
Most conventional video tape cassettes employ such flanged hubs thus lowering the mobility of a video tape recorder using such cassettes. Since there has been a strong demand for the mobility of video tape recorders to be improved so that recording and playback operations can be readily conducted outdoors, reduction of the size and weight of the cassette is a considerably important factor.
In order to solve this problem, a variety of microcassettes have been proposed in which the hubs are of a flangeless type which makes it possible to miniaturize the cassette. For instance, a small video tape cassette has been disclosed in Japanese Patent Application No. 154420/1976. The structure of the cassette is as follows: Engaging grooves are formed in the circumferantial wall of each of the flangeless cylindrical hubs with the grooves being arranged coaxially with the hub and extending from the lower surface of the hub to the midpoint of the hub. A cylindrical engaging wall extends upwardly from the inner surface of the lower half of the cassette engaging with the engaging grooves of each hub. The engaging wall has a height substantially equal to the height of the engaging grooves. The height of the engaging wall is selected so that, when the cassette is not being used, the bottom surface of the engaging grooves is in contact with the top surface of the engaging wall or the lower surface of the circumferantial wall of the hub is in contact with the inner surface of the lower half of the cassette. Protrusions and recesses are formed on the two contacting surfaces so as to stop the rotation of the hub in the unwinding direction of the tape. Urging means is provided acting on the hub so that the two surfaces are held in contact with each other. A specific feature of this small video tape cassette is that, when the cassette is not being used, the two surfaces are brought into contact with each other to prevent the unwinding of the tape on the hubs.
The above-described small video tape cassette, however, is disadvantageous in the following point: It is necessary to provide a space in the cassette in the hollow interior defined by the two halves of the cassette so that the engaging grooves are vertically completely out of engagement with the engaging walls to thus allow rotation of the hubs. Due to this, the thickness of the cassette (i.e. the dimension in the widthwise direction of the tape) cannot be reduced to the desired extent to thereby decrease the size and weight of the cassette.